500 million guests are caught up in Marriott Hotel hacking scandal
Some 500 million people around the world could be affected by a breach in the Marriott hotel chain's booking database.
The "data security incident" hit the system for its Starwood portfolio.
Work is continuing but the firm said the breached database contains the information of up to half-a-billion guests who booked before September 10.
The database stored information including passport numbers, dates of births, names, addresses and phone numbers for 327 million guests.
Payment card numbers and expiration dates were also stored for some.
Marriott Hotels owns a number of hotel chains, including the Ritz-Carlton and the Sheraton.
It also owns Dublin's Shelbourne Hotel - but it issued a statement yesterday saying it is not part of the Marriott's Starwood portfolio that has been affected.
Marriott-branded hotels use a separate reservation system on a different network.
Arne Sorenson, Marriott's president and chief executive, said the group deeply regretted the incident.
"We fell short of what our guests deserve and what we expect of ourselves.
"We are doing everything we can to support our guests, and using lessons learned to be better moving forward," he said.
"Today, Marriott is reaffirming our commitment to our guests around the world. We are working hard to ensure our guests have answers to questions about their personal information, with a dedicated website and call centre.
"We will also continue to support the efforts of law enforcement and to work with leading security experts to improve.
"Finally, we are devoting the resources necessary to phase out Starwood systems and accelerate the ongoing security enhancements to our network."
An investigation into the breach revealed that there was unauthorised access to the database on or before September 10, 2018.
Marriott has reported this incident to law enforcement and has already begun notifying regulatory authorities.
Personal finance exper, Laura Rettie from money.co.uk said that customers who were affected will be contacted, "however you should be super wary of anyone that says they're from either the Marriott or your bank or credit card provider".
"Unfortunately, fraudsters might take advantage of this being in the news and use it to gain more personal information from you.
"Stay on high alert and if you're suspicious hang up and call your bank or credit card provider directly. It's worth checking old bank statements and keep a close eye on future ones in the coming weeks and months for any activity you don't recognise."